'05 base model Taco 2.7 w/ P0300 n p0125

Alright guys, here it is. My check engine light has not come on at all, but codes P0300 and P0125 are stored in the historical codes file. I know because I checked with my scantool. I'm positive that the random miss is caused because of the coolant temp code, but I've seen posts (not for this particular year) that say it's the A/F sensor (pre-cat O2). I already checked it and it's cool. What I'm thinking is that since the code isn't actually a code just yet, the prob is intermittent, so I shook and tapped on the sensor, still nothin. I use ALLDATA for trouble shooting info, but they don't say anything about how to test the coolant temp sensor (ECT or CTS). All they say is check coolant level, make sure the fan isn't deformed, connections good, blah blah... If everything looks good, replace the ECT lol. ALLDATA DOES show how to test for resistance, but I'm guessing the ECT is okay because it's not throwing a code suggesting otherwise. Sooo, where should I go from here? I've been aware of this historic code for over 5 months and have been hoping my check engine light would come on, but nope lol. Thank you for ur time and help in advance!

 

Also, during winter the idle jumps to about 2200 for around 10 seconds, then dramatically drops to around 1500 and immediately goes back up. It's weird... I'd get a video of it, but it's pretty hot these days and hasn't done it since it's been cold here in Cali.

 

The rpm jump is normail when the engine is cold. My civic does this aswell

 

I'd agree man, but cold start isn't as dramatic. I've worked on a lot of production cars, and have never seen anything like this. I'm just surprised I haven't seen a check engine for it. Maybe because it only reveals itself during startup I guess.

 

After reading your information, you may try this. First I would clear all your codes out of the Computer. Second, I would clean your MAF and Your Throttle body and see if this helps your idle problem. A large jump in idle could come from a vacuum leak also, so you may check that out also. See if any of this helps, then we can go from there. Good Luck.

 

P0300 is for random missfires, meaning not a steady miss on a specific cylinder. I agree that looking into your p0125 code is a good idea, since the computer uses coolant temperature to control injector on-time, which is directly related to your air/fuel ratio.

P0125 shows that the system has detected insufficient coolant temp for closed loop. I would suggest checking your temp gauge. Does it seem to run cooler than you expected? If so, you may find that a VERY common problem for the p0125 is actually a stuck open thermostat, which slows down the engine warm-up when first starting. The fact that the codes are intermittent also supports this, as a sticky or partially clogged thermostat will cause an intermittent p0125.

My thoughts here anyway.

 

Thank you for your suggestions! I went ahead and cleaned my MAF n the throttle body, but it's still kind of hot here, so they prob won't occur at the moment. I will prob make another thread for this come winter time haha. I also tried to check around for a vacuum leak by spraying carb cleaner around, but no change in rpm ...

 

Your thoughts are always welcomed! My temp gauge (thankfully) is always in the mid haha. I also checked the temp that the ect was throwing and it seemed to be okay. It was around 176, which is normal according to alldata (again, thankfully lol). I also replaced my thermostat around 2 months ago, because I never had replaced it before and noticed that the thermostat COULD be a possible fix for the P0125. Still came up though, and I also deleted the code after the fix ... This ish has been bothering me. I don't want this thing to run too rich and jack up my O2's or CAT...

 

176 is around the bottom end of the thermostat range. One thing to notate, your temp gauge sensor and the sensor used for the computer are two different sensors on the Tacoma 4cyl. The one for the computer is in the back of the cylinder head, and the one for the gauge is behind the coil pack, screwed into the head.

Interesting thing! I just went into Mitchell1 service information and actually looked up the Toyota diagnostics for what the failure conditions are, and what can cause this code to set. According to Toyota, the P0125:
"DTC is set when sensor (Oxygen sensor) does not output a rich condition once engine is at normal operating temperature, engine speed of 1500 RPM or more, and vehicle speed is 25-62 MPH for at least 2 minutes."
According to Toyota, the most probably cause for this code is a faulty oxygen sensor (the one in the front of the cat)
I admit this is very different from the diagnostics of other manufacturers, but this is direct from Toyota.

 

Wow, thank you for this! ALLDATA has failed me lol... I will test the pre-cat O2 and let you guys know what I find. Thanks again!

 

Alright, I tested the O2 from pins 1 and 2 and it passed. However, I couldn't get the 2nd reading from 1 n 4, so I tried the same test on the post-cat O2 and didn't get a reading for that one either. I think there might be something up with my DMM. I checked the fuse n it was cool so I'm going to see if I can borrow my buddy's. I'm also replacing my rack n pinion today, so it's gunna b a long day lol.

 

pins 1 and 2 are the heater circuit, so that tests good? You do not check resistance if you are testing between 3 and 4. You want to measure voltage, as that is what the output from the sensor is. You need it set to scale for millivolts. With the sensor clean (no air from exhaust passing the sensor) You should be reading about 450 millivolts, which is the default standard. Any variation from that and you have a problem.

 

Yessir, 1 and 2 are good. Voltage test from pins 3 and 4 tested at 400 exactly with key on engine off. Is that within spec? Also, I meant the resistance test from pins 1 and 4. I tried to test it again, and I couldn't get a reading.

 

if you measure resistance between 1 and 4, you should get open circuit. there should be no connection. 1 and 2 are heater circuits, so the heater is good. Voltage being 400 mv between 3 and 4 is a tad low, and could cause an issue. Running voltage is what would help at this point, and the only way to see what the computer is getting is with a scan tool that can show you oxygen sensor output voltage. So far everything is within spec, but at the limit for the output at KOEO.

 

I'll try to check fuel trim once I get my rack back, because I had to get it RR'd. Thank you for the immense help Bama! I gotta read up on fuel trim again, because I only know the basics of reading them haha.

 

P.S., alldata makes me mad lol. It said that I should get around 10k ohms from 1 and 4... I'm going to check and see if Mitchell1 only sells subscriptions to shops haha

 

You can do the same with Mitchell1, where you can buy access to just one vehicle I believe. Other than that, I am on here all the time, so feel free to hit me up and I will be happy to look up whatever I can for whoever needs it. Just realize I have a business to run, so don't get mad if sometimes I don't reply too fast.

 

Sounds good, will do!

 

Alright, I know this thread has been dead for a while, but I have two new (readiness) codes now. They are P0171 (System too lean, Bank 1), and P0172 (System too rich, Bank 1). Here's a vid I recorded of some fuel trim PID's the other day. I kept revving the engine because I couldn't figure out why it would go into open loop after I let off the throttle. Anyways, here it is. http://www.youtube.com/watch?v=2fo_JqbV7eg